Plasmid load adversely affects growth and gluconic acid secretion ability of mineral phosphate-solubilizing rhizospheric bacterium Enterobacter asburiae PSI3 under P limited conditions.

Effect of the metabolic load caused by the presence of plasmids on mineral phosphate-solubilizing (MPS) Enterobacter asburiae PSI3, was monitored with four plasmid cloning vectors and one native plasmid, varying in size, nature of the replicon, copy number and antibiotic resistance genes. Except for one plasmid, the presence of all other plasmids in E. asburiae PSI3 resulted in the loss of the MPS phenotype as reflected by the failure to bring about a drop in pH and release soluble P when grown in media containing rock phosphate (RP) as the sole P source. When 100 μM soluble P was supplemented along with RP, the adverse effects of plasmids on MPS phenotype and on growth parameters was reduced for some plasmid bearing derivatives, as monitored in terms of specific growth rates, glucose consumed, gluconic acids yields and P released. When 10 mM of soluble P as the only P source, was added to the medium all transformants showed growth and pH drop comparable with native strain. It may be concluded that different plasmids impose, to varying extents, a metabolic load in the phosphate-solubilizing bacterium E. asburiae PSI3 and results in diminishing its growth and P-solubilizing ability in P deficient conditions.